GERTRUDE: Oh, he’s “our” son now, is he? Last time, it was all “your” son.
Also he’s not our son. He’s my son and your nephew and step-son, your nemesis, your thorn, your pea, your pearl, your trouble – but now, as he’s winning your bet for you, suddenly he’s “our” son.
I think the seed for Gertrude ignoring Claudius’ request that she not drink begins here. I think she’s pissed at him but is never in a position to say so.